1. Field of the Invention
The invention relates to an improved intra-aortic balloon catheter. More particularly, the invention relates to an intra-aortic balloon catheter having an improved catheter body and an improved kink-resistant inner tube that demonstrates improved guide wire tracking.
2. Description of the Prior Art
Intra-aortic balloon (IAB) catheters are used in patients with left heart failure to augment the pumping action of the heart. The catheters, approximately 1 meter long, have an inflatable and deflatable balloon at the distal end. The catheter is typically inserted into the femoral artery and moved up the descending thoracic aorta until the distal tip of the balloon is positioned just below or distal to the left subclavian artery. The proximal end of the catheter remains outside of the patient's body. A passageway for inflating and deflating the balloon extends through the catheter and is connected at its proximal end to an external pump. The patient's central aortic pressure is used to time the balloon and the patient's ECG may be used to trigger balloon inflation in synchronous counterpulsation to the patient's heart beat.
Intra-aortic balloon therapy increases coronary artery perfusion, decreases the workload of the left ventricle, and allows healing of the injured myocardium. Ideally, the balloon should be inflating immediately after the aortic valve closes and deflating just prior to the onset of systole. When properly coordinated, the inflation of the balloon raises the patient's diastolic pressure, increasing the oxygen supply to the myocardium; and balloon deflation just prior to the onset of systole lowers the patient's diastolic pressure, reducing myocardial oxygen demand.
IAB catheters may also have a central passageway or lumen which can be used to measure aortic pressure. Typical dual lumen intra-aortic balloon catheters have an outer, flexible, plastic tube, which serves as the inflating and deflating gas passageway, and a central tube therethrough formed of plastic tubing, stainless steel tubing, or wire coil embedded in plastic tubing. A polyurethane compound is used to form the balloon. In this dual lumen construction, the central lumen may also be used to accommodate a guide wire to facilitate placement of the IAB catheter and to infuse fluids, or to do blood sampling.
Very specialized materials, including Nitinol, have been used for the inner tube in an effort to reduce its outer diameter. A reduced diameter inner tube allows for a reduced diameter of the folded IAB membrane and thus allows for an easier insertion of the IAB catheter into the patient. The benefits of Nitinol include its high kink resistance and flexural stiffness at small wall thicknesses compared to the traditional polyurethane material used for prior art inner tubes. One major problem with Nitinol, however, is its high cost. Therefore, the need exists for an inner tube that is economical to manufacture and that has good kink resistance and flexural stiffness.
Another materials related problem encountered with dual lumen IAB catheters involves advancing the IAB catheter over the guide wire into the patient and also withdrawing the guide wire from the central tube after final placement of the IAB catheter. Friction between the outer surface of the guide wire and the inner surface of the central tube makes it difficult for the IAB catheter to track the guide wire. Therefore, the need exists for an IAB catheter, having an inner tube with a low coefficient of friction, that demonstrates improved guide wire tracking.
Co-pending U.S. patent application Ser. No. 08/958004 discloses an intra-aortic balloon catheter having a co-lumen extruded tube in which the inner lumen lies between the inner and outer surfaces of the catheter tube. As disclosed in that application a co-lumen arrangement allows for an increased gas path area. It is currently desired to achieve the same increase in gas path area but to allow for an inner tube which is made from a different material. Choice of a different material for the inner tube will allow for greater control of the kink resistance and flexural stiffness of said inner tube and of the entire catheter.
U.S. Pat. No. 5,711,754 by Miyata et al., discloses a balloon catheter having an inner tube affixed to the inner wall of the catheter tube by adhesion, melt-bonding, or integral formation. When affixed by integral formation, however, the catheter tube and the inner tube are comprised of the same material.
Yet another problem encountered with dual lumen IAB catheters is diffusion of gas or fluid from the outer lumen into the inner lumen. Any adulteration of the fluid within the inner lumen may corrupt blood pressure readings. Typically, the outer lumen of an IAB catheter contains a gas, such as Helium, and the inner lumen contains an incompressible column of fluid, such as saline, used for blood pressure measurements. The distal end of the saline column is in contact with the patient's blood and the proximal end of the column is in contact with a pressure transducer. The pressure reading of the pressure transducer correlates to the blood pressure of the patient. Any diffusion of a gas into the inner lumen increases the compressibility of the saline column thus affecting the blood pressure reading. Therefore, there is a need for a catheter designed to measure blood pressure without the aid of a potentially adulterated saline column.
While the IAB catheters presently on the market may be suitable for the particular purpose employed, or for general use, they would not be as suitable for the purposes of the present invention as disclosed hereafter.